Blowing agents for producing a cellular structure in polyurethane foams are typically added as a separate ingredient to the reactant package for fabricating the polyurethane. Water acts as a blowing agent by reacting with isocyanate to produce carbon dioxide and urea groups, this reaction is highly exothermic and is limited in its applicability in order to minimize the risk of foam scorch or fire.
Frequently, cellular and microcellular polyurethane foams are manufactured using chlorinated fluorocarbons (so-called "CFC's") as a blowing agent, alone or in combination with water, to blow the foam-forming reactants into the desired microcellular structure. Unfortunately, CFC's have recently come under attack for adversely affecting the ozone layer in the earth's atmosphere. As an alternative to the use of CFC's, so-called hydrogenated chlorinated fluorocarbons ("HCFC's") are being increasingly utilized in cellular and microcellular polyurethane foam manufacture. However, HCFC's are expensive and may also have some impact upon the earth's atmosphere. Accordingly, new alternatives to the use of CFC's and HCFC's as blowing agents for cellular and microcellular foams, particularly alternatives that are cheaper and do not adversely affect the environment, are highly desired by the polyurethane foam industry.
Various alternatives to the use of halocarbon blowing agents have been suggested in the past. By way of illustration, U.S. Pat. No. 4,417,002 discloses the use of carboxylic acid and salts of carboxylic acid as blowing agents for manufacturing polyurethane foam. Preferred blowing agents disclosed in the '002 patent include formic acid and salts of formic acid with weak organic bases such as hydrazine, triethylamine, dimethylbenzylamine and triethylenediamine. The '002 patent states that each mole of formic acid is converted, by virtue of its reaction with isocyanate, to one mole of carbon dioxide gas and one mole of carbon monoxide gas, with blowing being accomplished by means of these two gases. Although the use of carboxylic acids in accordance with the '002 patent is an alternative to the use of halocarbon blowing agents, the carboxylic acid does constitute a separate component in the reaction mixture.
As an alternative to the use of blowing agents which are separate components being added either to the reaction mixture or, more frequently, to the polyol-side of the reaction mixture, it would be highly desirable to provide reactants with built-in blowing capability. Heretofore, reactants possessing such built-in blowing capability have not been known, based upon the knowledge of the present inventors.